Telecommunications systems, cable television systems, and data communications networks use optical networks to rapidly convey large amounts of information between remote points. In an optical network, information is conveyed in the form of optical signals through optical fibers. Optical fibers comprise thin strands of glass capable of transmitting the signals over long distances with small loss.
Optical networks often employ wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) to increase transmission capacity. In WDM and DWDM networks, a number of optical channels are carried in each fiber at disparate wavelengths. Network capacity is based on the number of wavelengths, or channels, in each fiber and the data rates of the channels.
To increase the signal strength over long distances, optical communications systems typically include optical amplifiers at or between network nodes. The amplifiers typically include automatic gain control (AGC) to maintain a desired amplification factor (gain) across the amplifier. An optical amplifier may be used for each wavelength or channel transported by a fiber; however, using one amplifier for all wavelengths reduces system costs.